The long range objective of this research is to reach an understanding of molecular mechanisms that control mammalian sperm development. These studies will identify potential causes of human infertility and may suggest means to treat this problem. New approaches to male contraception are another possible benefit from research in this area. Interactions between germ cells and Sertoli cells in the seminiferous tubules are crucial for sperm development, but little has been learned to date about how these interactions are achieved at a molecular level. Protein-tyrosine kinases expressed in developing spermatocytes and spermatids are the focus of this application. Members of this enzyme family, through their roles in signal transduction, have been recognized as key regulatory molecules in the development of a variety of animal tissues and proteintyrosine kinases expressed in male germ cells are therefore strong candidates for roles as regulators of spermatogenesis. Through the use of a homology-based cDNA cloning strategy, a novel member of the protein-tyrosine kinase family, designated "PTK-Tl26", was identified that appears to be expressed in developing spermatocytes and/or spermatids. The specific research described in this application is designed to determine the mechanism that leads to the production of PTK-T126 and to characterize its cellular distribution and structural and biochemical properties. Specifically: structural features of PTK-Tl26 will be determined from an analysis of the amino acid sequence, which will be deduced from the nucleotide sequences of cDNA clones; the relationship between the testis-specific transcript that encodes PTK-Tl26 and a related, more widely expressed, transcript also will be determined through an inspection of cDNA sequences and by primer extension analysis; antibody reagents will be raised against PTK-Tl26 and will be used to detect the protein in testicular cells and to immunopurify the protein in order to assay for tyrosine kinase activity; and the potential for regulation of PTK-T126 expression at the translational level will be investigated by polysome analysis. The identification of other protein-tyrosine kinases expressed in developing male cells will also be pursued.